Apple has released a beta version of Safari 4 for Mac and Windows, with the most surprising thing being that the Windows version actually looks like a Windows program, and does Windows font rendering.

Like Google's Chrome and Android, the Nokia Series 60 and Palm webOS browsers, Safari is based on the Apple's WebKit open source rendering engine, and v4 is said to be the first browser to pass the Web Standards Project's tough Acid3 test. Safari 4 also features a new Nitro engine for rendering JavaScript, in response to Google Chrome's superfast JS processing.@Bill_Hodgson on Twitter, who runs Windows XP in Parallels, says Safari 4 is faster on both OS X and XP than Firefox 3 is on OS X. Whether it will be enough to tempt away people who love their Firefox extensions remains to be seen.

People who like Apple's bought-in CoverFlow technology should particularly like its use for viewing history and bookmarks in Safari 4, as well as presenting full-page previews. (Some have said it looks like a rip-off of CoolIris, but I don't use that, so I don't know how the two compare.)

It will be interesting to see how Safari 4's features and speed stack up against Internet Explorer IE8 RC1, Firefox 3 and Chrome -- or Opera, of course, though that has proven to be the browser you can't even give away. It certainly looks more appealing than Safari 3. But they are all have their merits, and users can choose whichever browser(s) they find most useful.

Update 1: Just been catching up with some test results, and CNet UK has not only run some, they've turned out some nice graphs. The story, Safari 4 benchmarked: 42x faster than IE 7, 3.5x faster than Firefox 3, says "our benchmarks confirm Apple's Safari 4 browser, released in beta today, is the fastest browser on the planet. In fact, it beat Google's Chrome, Firefox 3, Opera 9.6 and even Mozilla's developmental Minefield browser."

The tests were run with WebKit's SunSpider suite of JavaScript tests. But maybe they could also have tried Google's JavaScript test, which Google's Chrome used to win hands-down, according to CNet.

Of course, old testers know there are lies, damned lies and benchmarks, and they may not mean much. However, Safari 4 is certainly a snappy performer, and while racing through JavaScript hasn't done Chrome much good so far, it's definitely a welcome feature. Indeed, as more and more bloated JavaScript is dumped into memory by more and more underpowered web-based applications, the need for speed could become increasingly apparent.

Apple says Safari 4's 150 features are 'leading the way with innovation,' but in reality they're all things we've used before in other browsers — with Cupertino's magic aesthetic touch thrown in. Let's take a look at Safari's headliner features, what other browsers already have them, and how Safari's offering differentiates itself.

Also, in a comment below, KrisJones has posted a link to an image of benchmarks including the Google JavaScript tests.